Hepatitis C virus (HCV) is a common cause of chronic hepatitis, infecting approximately 4 million people in the United States and 170 million people worldwide. The vast majority of HCV-infected individuals develop chronic hepatitis C, which can progress to fibrosis, cirrhosis, and hepatocellular carcinoma. The study of the molecular mechanisms of HCV replication and hepatocarcinogenesis has been hampered by the lack of a small animal model of HCV replication and infection. Currently, chimpanzee is the only reliable animal susceptible to productive HCV infection and replication. However, the application of chimpanzee model is restricted by its limited resource and high maintenance cost. Our ability to develop alternative small animal models for HCV replication is constrained by the narrow host range of HCV infection. Recently, we have made significant advances in genetic studies of HCV replication and development of small murine models of HCV replication and infection. We have demonstrated that HCV RNA derived from a chromosomally integrated HCV cDNA resulted in robust production of infectious HCV. More importantly, we have found that HCV RNA replicated efficiently in the mouse embryo fibroblasts (MEFs). These advances allow us to hypothesize that the cDNA-derived HCV RNA can replicate efficiently in transgenic mice. The overall goal of this application is to develop transgenic mouse models for HCV RNA replication and to demonstrate HCV RNA replication in transgenic mice. Thus, we will develop multiple transgenic mouse lines that contain the cDNAs of a subgenomic and full-length HCV RNAs and a reversible tetracycline-controlled transcriptional activator (rtTA) and suppressor (tTS). Transcriptional expression of HCV RNA is under the control of a tetracycline-responsive promoter. HCV RNA replication in transgenic mice will be determined by multidiscipline approaches and will be validated by the use of HCV protease inhibitors and mouse interferons. Development of animal models that recapitulate HCV RNA replication, disease development and progression, and hepatocarcinogenesis will facilitate the determination of the roles and molecular mechanisms of host and viral factors in HCV replication, pathogenesis, and carcinogenesis. Moreover, the availability of transgenic HCV models will accelerate the discovery and development of prophylactic and therapeutic antiviral drugs and vaccines against HCV infection and thereby prevent HCC development. [unreadable] [unreadable] [unreadable]